Abstract: The computing of position region is very important in the application of rough set.Based on an in-depth study of rough set theory，mainly focusing on indiscernibility relation，a equivalent method for computing positive region is proposed.Then，the detailed descriptions of the algorithm for computing of positive region is analyzed based on universe decrement.The algorithm classifies samples in universe step by step and determines whether those samples belong to position region and deletes the samples from universe to reduce computational complexity.Finally，in order to test the efficiency of the algorithm，some experiments are made.And the theoretical analysis and experimental results show that this new method is much more efficient and useful in computing.

Key words: rough set, positive region, indiscernibility relation

摘要： 正区域的计算在粗糙集的应用中十分重要。在深入研究粗糙集基本理论的基础上，围绕不可分辨关系，得到了一种计算正区域的等价方法，提出了一种论域递减式的计算正区域的算法。该算法对论域中的样本进行分步分类，同时判断其是否属于正区域，而后将其从论域中删除，从而减轻计算量。理论分析和实例结果验证了该算法的有效性和可行性。

关键词: 粗糙集, 正区域, 不可分辨关系